IPv6 prefix delegation automatic null route - lost packets

Unanswered Question
Feb 24th, 2012
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I have an issue with IPv6 prefix delegation over PPPoE. When my router gets his v6-prefix delegated, it automatically creates a null route for this prefix. The problem is that I also have a static route to my firewall for the whole prefix, so now the router has two equal routes for the prefix (the null route and my static route). All devices behind my firewall loosing packages. How can I fix this?

Topology: [ISP-BRIDGE] -{PPPoE} fa0/0- [ROUTER] -fa0/1- [Firewall]

show ipv6 route

IPv6 Routing Table - default - x entries

Codes: C - Connected, L - Local, S - Static, U - Per-user Static route

       B - BGP, HA - Home Agent, MR - Mobile Router, R - RIP

       I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary

       D - EIGRP, EX - EIGRP external, ND - Neighbor Discovery


S   2001:DB8:1200::/48 [1/0]

     via 2001:DB8:1200:A000::3

     via Null0, directly connected


DHCPv6 prefix Debug output (proofs that the dhcp-client inserts the null route)

*Feb 24 17:25:52.959: [DHCPv6 client]IPv6RT[default]: static, Route add 2001:DB8:1200::/48 [owner]

*Feb 24 17:25:52.959: [DHCPv6 client]IPv6RT[default]: static, Added path ::/Null0

Configuration excerpt of my router

interface FastEthernet0/0

description Link-To-Bridge

no ip address

pppoe enable group 1

pppoe-client dial-pool-number 1


interface FastEthernet0/1

description Public

ip address

ipv6 address FE80::1 link-local

ipv6 address 2001:DB8:1200:A000::1/64


interface Dialer1

ip unnumbered FastEthernet0/1


encapsulation ppp

dialer pool 1

dialer persistent

dialer-group 1

ipv6 address autoconfig

ipv6 dhcp client pd ISP-PREFIX


ppp ipcp dns request


ip forward-protocol nd


ip route Dialer1


dialer-list 1 protocol ip permit

dialer-list 1 protocol ipv6 permit

ipv6 route 2001:DB8:1200::/48 2001:DB8:1200:A000::3

ipv6 route ::/0 Dialer1


Cisco IOS Software, 2801 Software (C2801-SPSERVICESK9-M), Version 15.1(4)M3, RELEASE SOFTWARE (fc1)


I found two other people with the same Problem, here and here. They both just configured two more specific routes. In my example it would be two /49 routes. But I don't think that is the proper solution for this problem.

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